Mask frames may be produced as a single piece punched from a steel band. On a first press, a plate is punched out from the steel band, the outer contour of which corresponds to the subsequent mask frame. From that plate, the mask frame is formed in another press. In a third step, the interior portion is punched out. The inner edge of the mask frame is flanged in a fourth step.
This punching method is disadvantageous because the interior portion of the steel band is not used. If the inner area, due to its small size, cannot be used for smaller mask frames, this material will be wasted, increasing the cost of manufacture.
Furthermore, it is already common practice to assemble a mask frame from multiple individual starting components by welding overlapping portions of the starting components. To this end, one or more band components are cut to proper lengths, for example. The ends of the components are overlapped and are welded together so that, in principle, a closed ring of metal band is formed. The required band width corresponds to the subsequent form of the mask frame. After welding, the ring is further processed using a punching technique.
The precondition of another familiar variant is that components with short limbs and of distinct shape, in the form of the Latin character U, for example, are punched in pairs. These parts are welded in an overlapping manner and then are further processed using a punching technique.
U.S. Pat. No. 3,516,147 describes bonding two components together by spot-welding. In U.S. Pat. No. 3,942,064, the overlapping ends of frame components a re welded together. The frame is assembled from both two and four components. Similarly,.the welding is carried out by spot welding.
Conventional welding procedures for producing mask frames are disadvantageous in that the bead of the weld seam which forms in both electric butt welding and pressure welding impedes the insertion of a welded mask frame into a drawing tool. This necessitates grinding or planing the protruding weld seams which, in turn, is quite time-consuming and limits automation in mask frame production. Also, pressure welding results in high energy consumption and increases the operating expenses in mask frame production.